VIE Consolidated Balance Sheet Detail (Details) $ in Thousands	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)
Variable Interest Entity
REDEEMABLE NONCONTROLLING INTERESTS	$ 613,336	$ 714,414	$ 664,757	$ 692,376
Consolidated Entity Excluding Variable Interest Entities (VIE) [Member]
Variable Interest Entity
Current Assets	(1,940,093)	(1,942,583)
Non-current Assets	5,954,266	5,945,353
TOTAL ASSETS	7,894,359	7,887,936
Current Liabilities	865,237	925,013
Non-current Liabilities	2,543,269	2,543,968
TOTAL LIABILITIES	3,408,506	3,468,981
REDEEMABLE NONCONTROLLING INTERESTS	590,531	597,274
Total Stockholders' Equity	3,895,322	3,821,681
TOTAL LIABILITIES AND STOCKHOLDERS' EQUITY	7,894,359	7,887,936
Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity
Current Assets	(38,396)	(131,869)
Non-current Assets	979	22,313
TOTAL ASSETS	39,375	154,182
Current Liabilities	273	1,044
Non-current Liabilities	0	0
TOTAL LIABILITIES		1,044
REDEEMABLE NONCONTROLLING INTERESTS	0	0
Total Stockholders' Equity	39,102	153,138
TOTAL LIABILITIES AND STOCKHOLDERS' EQUITY	$ 39,375	$ 154,182
Consolidated Investment Vehicles [Member]
Variable Interest Entity
Number of Funds	6	10		13
Consolidated Legg Mason, Inc.
Variable Interest Entity
Current Assets	$ (1,962,192)	$ (2,039,624)
Non-current Assets	5,955,245	5,966,496
TOTAL ASSETS	7,917,437	8,006,120
Current Liabilities	865,510	926,057
Non-current Liabilities	2,543,269	2,543,968
TOTAL LIABILITIES	3,408,779	3,470,025
REDEEMABLE NONCONTROLLING INTERESTS	613,336	714,414
Total Stockholders' Equity	3,895,322	3,821,681	$ 3,731,263
TOTAL LIABILITIES AND STOCKHOLDERS' EQUITY	7,917,437	8,006,120
Consolidation, Eliminations [Member]
Variable Interest Entity
Current Assets	16,297	34,828
Non-current Assets	0	(1,170)
TOTAL ASSETS		(35,998)
Current Liabilities	0	0
Non-current Liabilities	0	0
TOTAL LIABILITIES		0
REDEEMABLE NONCONTROLLING INTERESTS	22,805	117,140
Total Stockholders' Equity	(39,102)	(153,138)
TOTAL LIABILITIES AND STOCKHOLDERS' EQUITY	$ (16,297)	$ (35,998)
Sponsored Investment Fund [Member] | Consolidated Investment Vehicles [Member]
Variable Interest Entity
Number of Funds	0	2		2